As a semiconductor device, a memory element such as a DRAM (Dynamic Random Access Memory), a flash memory (storage device) and a device called a logic element having a storing section and a processing section are available. In recent years, a pattern for a semiconductor device tends to become increasingly fine and minute due to a trend of high speed processing, less power consumption, and increased storage capacity and, therefore, a demand for inspection of a defect occurring in a manufacturing process of semiconductor devices becomes severer at the same time. A defocus defect occurring in the exposure process in particular is a largest factor of defective products. The defocus defect refers to swelling of a wafer surface caused by foreign matters existing between a rear surface of a semiconductor wafer and a wafer stage which occurs at time of an exposure process and, as a result, a pattern line width and/or pattern diameter value being called a CD (Critical Dimension) value is out of dimensional tolerance resulting in pattern defects. Moreover, in a scanning-type exposure machine in particular, a focus change occurs in an exposure shot due to a focusing error which causes the CD value to be out of tolerance, also resulting in a defect in a pattern.
As an apparatus to automatically inspect a defocus defect, an apparatus to detect a defect in a pattern has been in practical use which is configured to irradiate a surface of a semiconductor wafer with illumination light to receive diffracted light from a repeating pattern on the surface of the wafer and to utilize a change in an amount of diffracted light occurring in the diffracted light from a defective portion (the change occurs due to difference in CD values) (see, for example, Patent Reference 1). The diffracted light is produced from a pattern of a repeating arrangement and its state depends on repeatability (cycle called an arrangement or a pitch). As a semiconductor device is becoming increasingly fine and minute, a repeating cycle of the repeating pattern (pitch) naturally becomes smaller and, in a memory device such as a DRAM, a transistor and/or capacitor has to be disposed in a small cell area and the arrangement of a repeating pattern (hole pattern) of a hole called a contact hole including a bit contact, capacitor contact (or called a storage node contact), cylinder contact (storage capacitor) and the like in one cell is two dimensional. Then, one cell further has an arrangement repeated two-dimensionally and, therefore, most of the surface of a memory device is occupied by two-dimensional repeating patterns.